title: Pressure-induced magnetic switching and linkage isomerism in K0.4Fe4[Cr(CN)6]2.8 x 16 H2O: X-ray absorption and magnetic circular dichroism studies.
abstract: The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% Cr(III)-N[triple bond]C-Fe(II) linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process.
authors.affiliation: Instituto de Ciencia Molecular, Universitat de València, Polígon La Coma s/n, 46980 Paterna, Spain. fmrm@uv.es
authors.forename: Eugenio
authors.initials: E
authors.lastname: Coronado
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Giménez-López
authors.forename: Tomasz
authors.initials: T
authors.lastname: Korzeniak
authors.forename: Georgiy
authors.initials: G
authors.lastname: Levchenko
authors.forename: Francisco M
authors.initials: FM
authors.lastname: Romero
authors.forename: Alfredo
authors.initials: A
authors.lastname: Segura
authors.forename: Valentín
authors.initials: V
authors.lastname: García-Baonza
authors.forename: Julio C
authors.initials: JC
authors.lastname: Cezar
authors.forename: Frank M F
authors.initials: FM
authors.lastname: de Groot
authors.forename: Alla
authors.initials: A
authors.lastname: Milner
authors.forename: Moshe
authors.initials: M
authors.lastname: Paz-Pasternak
mesh_terms: D017608:Chromium Compounds / Q000737:chemistry*; D003460:Crystallization; D003486:Cyanides / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry*; D007536:Isomerism; D008280:Magnetics; D011312:Pressure; D013057:Spectrum Analysis; D013696:Temperature; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D017608:Chromium Compounds; D003486:Cyanides; D058085:Iron Compounds; D014867:Water